1. Field of the Invention
The present invention relates to an alignment hub for a distributed generator system. In particular, the invention comprises an alignment hub for defining an alignment position between an engine and a single bearing generator and maintaining the alignment within a predetermined tolerance.
2. Background
Distributed generator systems, or gensets, are electric generating facilities used for a variety of purposes. Gensets are found in industry, home, marine and many other environments where there is a need to generate electricity. Most commonly a genset consists of an engine, typically an internal combustion engine, linked to an electrical generator.
The basic configuration of a genset comprises an internal combustion engine linked with some type of an adaptor to a generator. The adaptor forms a releasably secure connection that aligns the crankshaft of the engine to the rotor shaft of the generator. Power is transferred from the engine to the generator through this connection. In particular, with internal combustion engines a flywheel, which is an energy storage system in the form of a rotating mass mounted on a crankshaft of the engine, is connected to a flex plate located on the generator that can drive the rotor shaft of the generator. Through this connection, engine power is transferred to the generator for the purpose of generating electricity. Generally, the flex plate and the flywheel are joined together with a plurality of bolts located along the outer circumference of the two pieces. An adaptor plate is secured around the combination to secure and seal the connection between the flex plate and the flywheel.
Frequently, the engine used in gensets is diesel powered. Diesel engines operate most efficiently at relatively low rpms. For example, diesel engines used in gensets typically operate at 1500 rpms for 50-hertz power or at 1800 rpms for 60-hertz power. This power range works well for diesel engines, and places relatively little demand on the precision of the alignment between the engine and the generator. At such lows rpms, vibration resulting from improper alignment is not critical.
In some cases gasoline internal combustion engines have been used with gensets, however, the results have been less than successful. The optimum power range of gasoline engines is much higher than diesel engines. For example, gasoline engines normally operate at 3000 rpms for 50-hertz power or at 3600 rpms for 60-hertz power. Relatively high rpm operation creates a problem that is exacerbated by the drive to reduce engine emissions. A variety of devices have been developed to reduce the nitrous oxide (NOx) emissions. This is generally accomplished by making the engines run very lean. Internal combustion engines produce less power when running lean than when running stoichiometric. To produce more power means running the engines at even higher rpms.
The need to run at such high rpms places great demand on the alignment between the engine and the generator in a genset. The higher the rpms the more vibration that occurs. Also, due to the fact that gensets normally rely on diesel engines that run at low rpms the demand for precession alignment has been low, and techniques for alignment are poorly evolved. The worse the alignment the greater the vibration. Vibration causes excess wear, fatigues bearings, weaken points of connection, and presents a safety issue. Over time vibration can cause the bolts that connect the flywheel and the flex plate to fail, and the engine and generator can separate while operating. These components are typically large and heavy, and injury to property or person can easily result form such operational failure.
Generally, alignment is determined by the location holes on the flywheel and the flex plate. Perfect alignment results when the axis of rotation of the engine crankshaft is precisely coincident with the axis of rotation of the generator rotor shaft. In practice, the fact that the boltholes are not precisely machined, the perimeter location of the bolts holes, and play in the boltholes all contribute to poor alignment. The effect of the weight of the genset components also contributes to the alignment problem. The components are quite heavy, especially in larger gensets. This weight settles on the bolts and peens and distorts the boltholes, which quickly distorts the alignment. Furthermore, operational stress causes a similar problem.
As a result, the use of modem gasoline internal combustion engines, or any type of engine that operates at relatively high rpms, in gensets has been difficult to impossible due to the problems associated with alignment of the engine and the generator. Thus, a need exists for an improved apparatus and method of alignment.